1. Field of the Invention
The present invention relates to methods of reconstituting a time amplitude vs trace and, more particularly, to methods wherein the trace has been rectified by a scanner to produce a signal representative of a hardcopy display of the trace.
2. Setting of the Invention
During the acquisition of seismic data which is to be used in the exploration for hydrocarbons and minerals, large quantities of analog or digital data pulses are recorded on magnetic tape. These magnetic tapes are then processed to enhance the interpretability of the seismic data and most often, a hardcopy display of the seismic data, called a seismic section, is produced. The seismic section contains a plurality of wavy lines or traces formed on a time vs amplitude scale, which are then utilized by the skilled log analyst or geophysicist to determine if desirable hydrocarbons or minerals are located below the location where the seismic data was obtained. After the seismic section is produced, the processed seismic data is erased or destroyed so that the only remaining evidence of the seismic data is the seismic section.
If at a later date reprocessing of the seismic. data is desired, the original form of the seismic section must be reconstituted or regenerated. One manner to accomplish this is to use an optical scanning device that is passed over each trace to reconstitute the data in an analog wave representative of the original form, as is well known in the art. A problem arises in this instance because most optical scanning devices are only capable of reproducing the positive values of the waveform, i.e. the negative values of the waveforms cannot be determined or reconstituted by this manner. Further, oftentimes the amplitudes of the traces above a certain maximum value are clipped, i.e., removed or flattened. An example of a signal which has no negative values and which has been amplitude clipped as from an optical scanner is shown in FIG. 1. The signal is shown in solid lines while the missing portions of the original signal is shown in dotted lines.
Obviously, the above-described deficiencies with the reconstituted signals can cause poor response to subsequent seismic processing methods, such as filtering, automatic event detection or "picking", or amplitude manipulation. There exists a need for a method of reconstituting the entire signal from an optical scanner.
Prior art methods of signal reconstituting are disclosed in U.S. Pat. No. 4,192,003, Brock, et al.; U.S. Pat. No. 4,455,613, Shoemaker; and U.S. Pat. No. 4,462,083, Schwefel. All these methods utilize interpretations of the peaks of the signal by measurement of the slopes of the different wave angles adjacent the portions of the signal to be reconstituted. These methods are useful in reconstituting signals from traces that have a high noise-to-signal ratio. However, these prior art methods cannot be utilized to reconstitute signals that contain both (a) no negative values and (b) clipped amplitudes because the methods cannot reconstruct the negative portions of the signal, given only positive portions.